1. The Field of the Invention
The invention generally relates to aligning optical components. More specifically, the invention relates to aligning a TO can, including a photodiode, in a receptacle.
2. Description of the Related Art
Fiber-optic communication is used to transmit digital signals. The signals are converted to and from light signals which are then transmitted and received along fiber-optic cables. The fiber-optic cables are generally glass and/or plastic waveguides that allow for the propagation of optical signals along the fiber-optic cables.
A light emitting diode (LED) or laser is often used to convert the digital signal to an optical signal. The LED or laser is often included in an optical component known as a transmitting optical subassembly (TOSA). The TOSA modulates the laser according to a digital electronic stream received at the TOSA to produce a modulated optical signal. This modulated optical signal is sent along a fiber-optic cable to a receiver optical subassembly (ROSA).
A ROSA generally includes a photodiode or other light-sensitive device connected to a transimpedance amplifier (TIA). Light from the optical signal impinging the photodiode causes a current to pass through the photodiode where the current corresponds to the amount of light impinging the photodiode. The TIA converts the current running through the photodiode to an electronic signal usable by a digital device such as a computer, network router and the like.
It is desirable to manufacture TOSAs and ROSAs such that they can be implemented quickly and efficiently in an optical network. Thus, the TOSA and ROSA often include fixed receptacles, such as LC, SC and the like, that allow the fiber-optic cables to be plugged into the receptacle such that the fiber-optic cables are properly aligned for receiving and delivering optical signals.
In the example of a ROSA, the photodiode is often encapsulated in a transistor outline (TO) can where the TO can also encapsulates supporting circuitry for the photodiode such as the TIA. The TO can often includes a transparent top surface for receiving optical signals at the photodiode. To couple a receptacle to the TO can, a high frequency optical signal is directed into the receptacle while the TO can is manipulated in the barrel of the receptacle until the highest amount of coupling of the optical signal into the photodiode occurs. The TO can may then be epoxied or otherwise fixed in the barrel of the receptacle such that it is in an optimum position for receiving optical signals.
The ROSA may be designed to receive optical signals that are in the 1 gigabit per second and higher range. Alignment techniques have typically used a 1 gigabit per second or higher signal directed into the photodiode to align the TO can in the barrel for maximum optical coupling. Unfortunately, expensive test equipment must be used to monitor the signal in the ROSA for determining when the maximum optical coupling occurs because of the high frequencies used when aligning.
What would be useful is test equipment that can test ROSA alignment using lower frequency or DC optical signals.